Effect of stimulus parameters on characteristics of the F-response in normal subjects

The F-response is a valuable tool for evaluating the functional integrity of proximal nerve segments. Although many studies have focused on the various F-response characteristics observed (e.g., latency, amplitude, duration, persistence, etc.), few have examined the significance of stimulus parameters on the resultant F-response. In this study, we examined the F-responses obtained in 25 healthy subjects when using various stimulus parameters. The stimulus parameters used were: 1) 0.5 Hz, 25% supramaximal intensity at 0.05 ms duration; 2) 0.5 Hz, 25% supramaximal intensity at 0.1 ms duration; 3) 0.5 Hz, 25% supramaximal intensity at 0.2 ms duration; 4) 0.5 Hz, 50% supramaximal intensity at 0.1 ms duration; 5) 3.0 Hz, 25% supramaximal intensity at 0.1 ms duration. No significant differences in F-response latency, amplitude, duration or persistence were seen when duration or intensity of stimuli was altered. However, changing stimulus frequency resulted in a significant decrease in latency and a significant increase in persistence and amplitude. Care should be taken in controlling for stimulus frequency to enhance the reproducibility of F-response determinations.